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In-Depth From A.D.A.M. Background

Vitamins do not share a common chemistry, but they do share certain characteristics. They are all organic nutrients that are necessary in small amounts for normal body functioning and good health. Your diet or any supplements you take provide most vitamins. The body can manufacture only three vitamins (D, K, and the B vitamin biotin) from nondietary sources. Unlike carbohydrates, fats, and proteins, vitamins are not sources of energy. Instead, vitamins are chemical partners for the enzymes involved in the body's metabolism, cell production, tissue repair, and other vital processes.

Vitamins are either fat soluble or water soluble. The fat-soluble vitamins, which include A, D, E, and K, are absorbed by the body using processes that closely parallel the absorption of fat. They are stored in the liver and used up by the body very slowly. The water-soluble vitamins include vitamin C and the B complex vitamins. The body uses these vitamins very quickly. Excess amounts are eliminated in urine.

Guidelines for Adequate Intake of Vitamins

The Recommended Dietary Allowance (RDA) for vitamins, set by the Food and Nutrition Board of the National Academy of Sciences-National Research Council, has been used for years as a guide for determining the amount of vitamins needed to prevent deficiency diseases. The RDA refers to an estimate of the average requirements of dietary components such as calories, vitamins, minerals, and proteins that are required to prevent deficiency. Different values apply to different groups based on gender and age.

The RDA is gradually being replaced by a new standard called the Dietary Reference Intake (DRI). The DRI represents a shift in nutritional emphasis -- from preventing deficiencies to lowering risks of chronic diseases, such as cardiovascular disease. The DRI values comprise four categories:

The recommended dietary allowance (RDA). This is the current rating on most vitamins.

The estimated average requirement (EAR). This is the amount that will meet the nutritional requirements of 50% of the population.

Adequate intake (AI). This is an amount that will be used if there is insufficient data to calculate the RDA.

Tolerable upper intake level (UL). This is the maximum dose likely to be safe in 98% of the population.

Food and supplement labels now typically list the Daily Value (DV). This is the percentage of the amount of a nutrient that experts believe a person needs in their daily diet. On food labels it is usually based on one serving size for a person who takes in 2,000 calories a day.

Regulating Quality

Regulation of dietary supplements by the U.S. Food and Drug Administration (FDA) is a complex issue.

Labels on vitamins and other dietary supplements now include nutrient information and list all ingredients, including identifying parts of plants from which ingredients may be taken. Unlike the labels for drugs, however, labels for vitamins and supplements may not claim to prevent or treat any specific disease. Labels for vitamins and supplements include one of the following:

Health claim
-- description of how the substance may reduce the risk of a health-related condition

Nutrient claim
-- description of the amount of the nutrient in the product or

Structure or function claim
-- description of how the product may affect organs or systems of the body, without claiming to prevent or treat specific disease

The quality of dietary supplements depends on the manufacturer and is not regulated by FDA. The U.S. government does not require that supplements be standardized, meaning that the amounts or quality of nutrients may vary depending on the batch. So, more expensive supplements are not necessarily better than the less expensive ones. Government regulations are in the process of catching up to the boom in the supplement industry. In the meantime, some companies voluntarily adhere to rigorous quality controls, while others do not.

The U.S. Pharmacopeia (USP), an independent organization that sets quality standards for drugs, has also implemented standards for vitamins. Consumers may look for the USP label on products of companies that adhere to these standards. USP verification means the following:

What is in the bottle matches what is listed on the label.

There are no harmful levels of contaminants.

The supplement will be absorbed properly into the body.

It has been produced according to good manufacturing standards.

The FDA does not require manufacturers to provide any scientific evidence that dietary supplements are safe and effective before a product is sold (unlike drugs, which must be proven both safe and effective through clinical trials). If a supplement causes side effects in people once it is for sale, the government may place restrictions on the supplement or withdraw it from the market. The FDA may also withdraw products from the market if their labels are misleading or false.

People Who Should Take Vitamin Supplements

About 30% of Americans take at least one vitamin or mineral supplement daily. However, studies evaluating the population as a whole found that there was no difference in mortality rate between those who took vitamin supplements and those who didn't. Most people who have a healthy diet do not need vitamins, but there are some exceptions.

Pregnant and Breast-feeding Women.
Women who are pregnant or who are breast-feeding generally need additional vitamins. Folic acid and vitamins B6 and B12 are particularly important. Women who are vegetarians must be sure to avoid vitamin B12 deficiencies, which can harm their offspring. Folic acid reduces the risk for neural tube defects and possibly facial abnormalities, such as cleft palate. Studies also show that low folate levels during pregnancy are associated with low birth weight, a risk factor for the development of cardiovascular disease in adulthood. A woman's best approach is to take extra folic acid plus multivitamin supplements (which have additional benefits), starting them before becoming pregnant.

The human body stores several years' worth of vitamin B12, so nutritional deficiency of this vitamin is extremely rare. However, people who follow a strict vegetarian diet and do not consume eggs or dairy products may require vitamin B12 supplements.

Pregnant women with healthy diets may have low folate levels and need to take supplements. Requirements are as follows:

The recommended dietary allowance (RDA) for folic acid prior to conception is 400 mcg, and during pregnancy it is 600 mcg.

During breastfeeding 500 mcg is recommended.

Some women have low vitamin A reserves in their liver. It is important to note, however, that too much vitamin A significantly increases the risk for birth defects. Daily amounts of 10,000 IU (international units) of vitamin A in supplements and food can pose a danger. Experts recommend that pregnant women take in no more than 2,500 IU/day and avoid eating liver.

Infants and Children.
Infants who are breast-fed by healthy mothers receive enough vitamins except, in some cases, vitamins K and D. Human milk has low levels of vitamin K, and the newborn's immature intestinal tract may not produce enough of the baby's own supply. Most babies are given an injection of this vitamin at birth. Infants being breast-fed by malnourished women or those who lack sufficient exposure to sunlight may be deficient in vitamin D. In these cases, supplements of 200 - 300 IU are recommended.

Formulas are required to contain sufficient vitamins and minerals. Beyond infancy, most American children receive all the vitamins they need from their diet, unless they are living in severely deprived circumstances.

Smokers.
Smoking interferes with absorption of several vitamins, importantly vitamins C and D. Smoking can interfere with the metabolism of vitamin D, resulting in poor muscle function.

Taking high doses of antioxidant vitamins, especially beta carotene, is harmful to smokers. Instead of taking supplements, smokers should be sure their diets are rich in fresh fruits, vegetables, and whole grains. Of course, smoking cessation is the most important intervention of all.

Alcoholics.
Alcoholics often suffer from multiple vitamin deficiencies. The most dangerous deficiencies are in vitamins B1 (thiamin), folic acid, B6 (pyridoxine), B2 (riboflavin), and vitamin C. Low levels of vitamin B6 are associated with increased risk of colorectal cancer in men who drink large amounts of alcohol.

People Who Have Had Gastric Bypass Surgery
. Vitamin deficiency is a recognized complication of gastric bypass surgery. Women, African-Americans of both sexes, and adults who have had laparoscopic Roux-en-Y bypass surgery are at highest risk. The deficiency is treated with water-soluble vitamin supplements.

Strict Vegetarians
. Strict vegetarians need supplements of vitamin B12, unless they get enough of it from fortified cereals and other grain products.

Dieters and Vegetarians.
People on weight-reduction diets with less than 1,000 calories a day should probably take a multivitamin and should also check regularly with a physician.

Vegetarians may need riboflavin, vitamin B12, and vitamin D supplements. Vegans, who do not eat dairy or eggs as well as meat, may be at further risk for vitamin A deficiencies if they do not also have plenty of dark colored fruits and vegetables. Those who eat eggs and dairy products need only watch their iron levels.

Deficiencies in vegetarian children may be particularly harmful. (One study, for example, reported that adolescents who had been on macrobiotic diets before age 6 and were deficient in vitamin B12 scored lower on psychological tests.) Pregnant and breast-feeding women who are vegetarians must be sure to have sufficient vitamins. Of special note, maternal deficiencies in vitamin B12 may cause delayed growth and neurologic problems in newborns.

Older Adults.
Deficiencies of vitamins and important minerals have been observed in almost a third of elderly people. Often their dietary habits slip and they fail to eat balanced meals regularly. In addition, older adults are more likely to be taking medications for a variety of conditions. Multiple drug regimens may prevent absorption of some vitamins. Elderly people, particularly if they are not exposed to sunlight, may be deficient in vitamin D. They also may have low levels of important B vitamins. (Older adults showing signs of dementia should be checked for B12 deficiencies as well as other disorders causing mental disturbances.) One study reported that the immune systems of elderly people may benefit from higher levels of vitamin E than the dietary recommended dosage. It should be noted, however, that metabolism slows down as a person ages, and in elderly people it takes the liver longer to eliminate drugs and vitamins from the body. The effect of some vitamin supplements, therefore, may be intensified. Dosage levels of vitamin A, for instance, which might be harmless in a younger adult, could be toxic in an elderly patient.

People Who Avoid Sunlight.
People who avoid sunlight or are housebound, and whose diet is low in foods that contain vitamin D should take supplements. People with darker skin are at higher risk for deficiencies than those with whiter skin. (Note: vitamin D is toxic in high doses, and no one should exceed the recommended dietary intake of vitamin D except under the direction of a physician.)

For pregnant women: 2,500 IU for pregnant women under 18; 2,565 IU for pregnant women over 19. (Upper limit is 9,335 IU for ages 14 - 18 and 10,000 IU for women over 19. It should be noted that some experts recommend 8,000 IU as the upper limit during pregnancy.)

Warning: Use of preformed vitamin A, including the skin acne medication tretinoin (a vitamin A derivative), during pregnancy can cause birth defects.

Note: In determining the daily vitamin A allowance, experts also take note of provitamins, such beta carotene, that convert to vitamin A. Some experts recommend 3 - 6 mg of beta-carotene.

Vitamin A is also now being measured with a new unit called the Retinol Activity Equivalent (RAE). One RAE is equal to 1 mcg retinol, 12 mcg beta-carotene, 24 mcg alpha-carotene, and 24 mcg beta-cryptoxanthin. Retinol is the most active form of vitamin A.

Foods containing the vitamin

Animal products, such as liver, dairy products, eggs, and fish liver oil. Provitamin A carotenoids are also found in dark red, green, and yellow vegetables and fruits. Requires some dietary fat to be absorbed.

Effects of deficiencies

Skin disorders, severe diarrhea, and eye damage. In less developed countries severe deficiencies cause blindness in 250,000 children each year. Diets low in vitamin A may also increase the risk of developing cancer. Low dietary intake of vitamin A has been associated with impaired lung function in children.

People at risk for deficiencies

Preschool children and any child with inadequate intake of protein, calories, and zinc. Iron deficiency may also impair metabolism of vitamin A.

People with asthma.

People with serious disorders in the intestine, liver or pancreas, such as cystic fibrosis, steatorrhea, biliary obstruction, inflammatory bowel disease, cirrhosis, and others.

People who have undergone Roux-en-Y gastric bypass surgery.

Vegans (vegetarians who do not eat eggs and dairy). Such individuals should be sure to have plenty of deep-colored fruits and vegetables.

People who abuse alcohol. It should be noted, however, that although people with alcoholism may be at risk for vitamin A deficiency, a combination of high-dose vitamin A and alcohol may cause toxic liver damage.

Healthy adults usually have a year's store of vitamin A in the liver, so temporary nutritional deficiencies or problems with fat absorption are unlikely to cause serious vitamin A deficiency problems.

Toxicities

Even moderately high doses appear to increase the risk of hip fractures.

Very toxic when taken in high-dose supplements for long periods of time.

Can affect almost every part of the body, including eyes, bones, blood, skin, central nervous system, liver, and genital and urinary tracts. Severe toxicity can cause blindness and may even be life threatening. In children, chronic overdose can cause fluid on the brain and as well as the same complications seen in adults. High consumption of vitamin A may also increase the risk of gastric cancer, osteoporosis, and fractures in both men and women.

Pregnant women who take amounts not much higher than RDA levels increase the risk for birth defects in their children. Liver damage can occur in children who take RDA-approved adult levels over prolonged periods of time or in adults who take as little as five times the RDA-approved amount for 7 - 10 years.

RDA is 0.5 mg/day for children aged 1-3 years, 0.6 mg/day for children aged 4-8, 0.9 mg/day for children aged 9-13, 1.2 for teen boys and men (ages 14 and up), 1 mg/day for girls aged 14-18 years, and 1.1 mg for women aged 18 and older. The RDA for pregnant and nursing women is 1.4 mg/day.

Foods containing the vitamin

Best source is pork and good sources are dried fortified cereals, oatmeal, corn, nuts, cauliflower, and sunflower seeds. Supplements for people with normal diets and good health are unnecessary.

Effects of deficiencies

Deficiencies are uncommon in the U.S., but when they occur, they usually involve several B vitamins, since many of them come from the same food groups.

Severe vitamin B1 deficiency is known as beriberi. It can cause visual disturbances, paralysis, staggering, loss of sensation in the legs and feet, psychosis, and congestive heart failure.

People at risk for deficiencies

Alcohol interferes with these vitamins, and some of the physical and mental problems that alcoholics experience may be attributed to a deficiency of B vitamins. Elderly people are also at risk for deficiencies because of inadequate diets and potential interference with B-vitamin absorption by medications. Deficiencies can occur in severely malnourished people or in those receiving long-term dialysis or intravenous feeding. Vegetarians may be at risk.

See general vitamin B description.

Toxicities

Because the B vitamins are water-soluble and eliminated in the urine, toxic reactions from oral administration of most of them are extremely rare. (Exceptions are niacin and vitamin B6.) It should be noted that substances known as B15 (pangamic acid) and B17 (laetrile) are neither vitamins nor nutrients; both chemicals are highly dangerous and have no proven nutritional or health value.

RDA is O.5 mg/day for children aged 1-3 years, 0.6 mg/day for children aged 4-8, 0.9 mg/day for children aged 9-13, 1.3 for teen boys and men (ages 14 and up), 1 mg/day for girls aged 14-18 years, and 1.1 mg for women aged 18 and older. The RDA for pregnant women is 1.4 mg/day and for nursing women 1.6 mg/day.

RDA is 6 mg/day for children aged 1-3 years, 8 mg/day for children aged 4-8, 12 mg/day for children aged 9-13, 16 mg/day for teen boys and men (ages 14 and up), 14 mg/day for girls aged and women aged 14 and older. The RDA for pregnant women is 18 mg/day and for nursing women 17 mg/day.

AI is 2 mg/day for children aged 1-3 years, 2 mg/day for children aged 4-8, 4 mg/day for children aged 9-13, and 5 mg/day for teens and adults (ages 14 and up). The AI for pregnant women is 6 mg/day and for nursing women 7 mg/day.

Whole grains, beans, milk, eggs, and liver. Supplements are unnecessary in people with normal health and diets.

Effects of deficiencies

Deficiencies affect the skin and mucous membranes and can cause cracks on the lips or corners of the mouth, eczema of the face and genitals, a burning sensation on the tongue, eye irritation. May contribute to anemia when iron levels are low and contribute to elevated levels of homocysteine, a heart risk factor.

Deficiency is unlikely except in company with other B vitamin deficiencies. Symptoms include abdominal distress, burning sensation in the heels, and sleep problems.

People at risk for deficiencies

See general vitamin B description.

Alcoholics and any malnourished persons.

Alcoholics and any malnourished persons.

Toxicities

No toxic effects had been reported even from large doses of riboflavin.

Even mildly high doses of niacin can cause hot flushing of the face and shoulders, headache, itchiness, and stomach problems. Some report heart disturbances and temporarily lowered blood pressure. Large doses may produce ulcers, gout, diabetes, and liver damage, which are usually reversed when high doses are discontinued.

Although no toxicity has been reported in humans, high dosages have caused liver damage in rats.

RDA is O.5 mg/day for children aged 1-3 years, 0.6 mg/day for children aged 4-8, 1 mg/day for children aged 9-13, 1.3 for teen boys and men ages 14-50. and 1.7 mg/day for men aged 50 and up; 1.2 mg/day for girls aged 14-18 years, 1.3 mg for women aged 18-50, and 1.5 mg/day for women aged 50 and up. The RDA for pregnant women is 1.9 mg/day and for nursing women 2 mg/day.

RDA is 0.9 mcg/day for children aged 1-3 years, 1.2 mcg/day for children aged 4-8, 1.8 mcg/day for children aged 9-13, and 2.4 for teens and adults ages 14 and up. The RDA for pregnant women is 2.6 mcg/day and for nursing women 2.8 mcg/day.

The only natural dietary sources are animal products, including meats, dairy products, eggs, and fish (clams and oily fish are very high in B12). Like other B vitamins, however, B12 is added to commercial dried cereals and fortified grain products.

In unborn children, some evidence shows that lack of vitamin B6, in addition to vitamin B12 and folic acid, may be responsible for defects such as cleft lip and palate and spina bifida. Supplementation with these vitamins is advised during pregnancy.

Note: People who have been taking more than 50 mg for some time and stop suddenly are at risk for a so-called rebound deficiency. When people stop, they should taper off slowly.

Children who are deficient may experience growth failure. Deficiencies in pregnant and breast-feeding women may cause neurologic harm in their offspring.

A genetic defect that causes vitamin B12 deficiencies is responsible for pernicious anemia, a serious disorder that causes rapid heart rate, shortness of breath, dizziness, weakness, and fatigue. It must be treated with injections of vitamin B12 or very high oral doses to prevent neurologic damage.

People at risk for deficiencies

Alcoholics and any malnourished person. In rare cases, infants are born unable to metabolize pyridoxine; in such cases, seizures or convulsions can occur and vitamin B6 must be administered.

Nearly 30% of patients with inflammatory bowel disease have vitamin B6 deficiency, as well as low levels of iron and vitamin D.

People who take the antibiotic isoniazid, high blood pressure medication hydralazine, and the drug penicillamine are at risk for vitamin B6 deficiency.

The elderly and people with Crohn's disease and those who have undergone ileal and ileocolonic resection may have trouble absorbing natural vitamin B12 and require supplements.

Studies have found that patients with diabetes treated with metformin, but not rosiglitazone, are at risk for low levels of vitamin B12.

Vegetarians are at higher risk for deficiencies.

Toxicities

Very high doses can cause nerve damage with symptoms of instability and numbness in the feet and hands, which may be permanent in some cases. Of specific concern are possible adverse effects on nerve development in the offspring of pregnant women who take large doses, such as for morning sickness.

Important for many metabolic processes in the body. It is used in the manufacturing of neurotransmitters (chemical messengers in the brain), in protecting the heart, and for synthesizing genetic materials (DNA) in the cells. It may improve blood flow.

AI (daily) is 8 mcg in children 1-3 years of age, 12 mcg in children 4-8, 20 mcg for children 9-13, 25 mcg for children aged 14-18, and 30 mcg for anyone over 18, including pregnant women. The AI for nursing women is 35 mcg/day.

AI (daily) is 200 mg in children 1-3 years of age, 250 mg in children 4-8, 375 mg for children 9-13, 550 mg for boys and men aged 14years and up, 400 mg for girls aged 14-18 years, and 425 for women older than 18. The AI for pregnant women is 450 mg/day, and 550 mg/day for nursing women.

Supplements may be
folate
(natural) or
folic acid
(synthetic). Folic acid is nearly twice as potent as folate.

RDA is 400 mcg
folate
for ages 14 and up, 600 mcg during pregnancy and 500 mcg while nursing. The DRI for children aged 1-3 is 150 mcg/day, 200 mcg for children aged 4-8 years, and 300 mcg for children aged 9-13.

Women who are planning to be pregnant should certainly take 400 mcg of folic acid before conception, during pregnancy, and while nursing.

Foods containing the vitamin

Dietary sources are eggs, milk, liver, mushrooms, bananas, tomatoes, whole grains, nuts, and brewer's yeast. Also produced by bacteria in the intestines.

As with vitamins B6 and B12, deficiencies of folate elevate levels of homocysteine, an amino acid in the body that may increase the risk for heart disease, and possibly Alzheimer's disease. Folic acid supplements lower homocysteine levels, but with little or no impact on risk of atherosclerotic disease in the heart or in the peripheral arteries and veins. This suggests that homocysteine may be a marker of cardiovascular disease, rather than a cause. This being said, some evidence suggest that folic acid supplementation in patients with low folic acids levels substantially reduced the risk of a first stroke.

Low levels during pregnancy increase risk of birth defects in newborns, and folic acid supplementation plays a key role in preventing birth defects. Folic acid deficiencies can also cause depression, megaloblastic anemia, and impairments in concentration, memory, and hearing.

People at risk for deficiencies

Alcoholics, malnourished persons, people with conditions that disrupt the normal functioning of the small intestine, people taking certain drugs, particularly methotrexate. Other risk factors for deficiency: high-dose aspirin, smoking, treatment for seizures, taking oral contraceptives.

Toxicities

Excessive doses can cause intestinal problems, and there is also some concern that high doses can be carcinogenic.

Possible connection between high consumption of folate/folic acid and colorectal and prostate cancers now under exploration.

Some link between high doses and central nervous system disorders, zinc deficiency, and seizures in epileptics. This risk appears to be low, but results indicate that megadoses should be avoided. High amounts in the elderly may mask symptoms of vitamin B12 deficiencies.

Vitamin C (Ascorbic Acid)

Benefits

Vitamin C is a water-soluble vitamin. Acts as an antioxidant (reduces harm from damaging chemical processes in the body). Essential for the production of collagen, the basic protein in bones, cartilage, tendons, and ligaments.

Other possible benefits include protection against bronchoconstriction during exercise in people with asthma. May help boost the immune system.

Orange juice is the most important source of vitamin C in the U.S., with frozen juice being the best source of the vitamin.

Effects of deficiencies

Scurvy is the primary deficiency disease. Affects most body tissues, particularly bones, teeth, and blood vessels. Early symptoms include tiredness, weakness, irritability, weight loss, and vague muscle aches. Later symptoms are bleeding gums, wounds that won't heal, rough skin, and wasting away of the muscles. Deficiencies may contribute to periodontal disease and gallstones. Low dietary intake of vitamin C has been associated with impaired lung function in children. Low intake may also increase lead levels in the blood.

People at risk for deficiencies

Deficiency has been uncommon in the U.S., usually occurring in the elderly, alcoholics, cancer patients, and some people on severely limited diets low in fresh fruits and vegetables. Surprisingly, however, studies now suggest that as many as 16% of middle-aged Americans, with the highest risk being smokers and middle aged men, are deficient in vitamin C. High doses of aspirin taken over a long period of time can interfere with vitamin C.

Toxicities

Tolerable upper limit is 2000 mg/day in adults (the limit is lower in children). High doses may cause headaches and diarrhea. Long-term high doses may increase risk for kidney stones. Ascorbic acid increases iron absorption so people with blood disorders, such as hemochromatosis, thalassemia, or sideroblastic anemia, should avoid high doses. Large doses may also thin blood and interfere with anticoagulant medications, blood tests used in diabetes, and stool tests. Rebound scurvy can occur after abrupt withdrawal from long-term large doses. This rebound effect may especially affect infants or pregnant women.

Vitamin D

Benefits

Vitamin D is actually a single term for several hormones that are stored mainly in the liver and also in fat and muscle tissue. It is essential for the absorption of calcium into the bone and for normal bone growth.

AI (daily) is 200 IU (5 mcg) for children and most adults to age 50, 400 IU (10 mcg) for people between ages 50 and 70, and 600 IU (15 mcg) over age 70. Note that many experts currently recommend a dose of 800 - 1000 IU daily for adults. People who are housebound, do not have sufficient exposure to sunlight, or are dark-skinned, as well as breast-fed infants, should take vitamin D supplements. The maximum tolerated dose after the age of 12 months is 2,000 IU/day (50 mcg/day). Note that the American Academy of Pediatrics recommended in November 2008 that the minimum intake for children and adolescents be changed to 400 IU / day.

How the body gets the vitamin

There are two forms of vitamin D. Vitamin D3 is made in the body from a chemical reaction to the ultraviolet radiation in sunlight. Vitamin D2 is found in a few food sources, including vitamin D fortified milk, fatty fish, egg yolk, and liver.

Effects of deficiencies

Softening of the bones caused by low levels of calcium and phosphorous (called rickets in children and osteomalacia in adults). Also increases the risk for bone-related knee problems, and hip fractures in postmenopausal women. Associated with a higher risk for prostate cancer and breast cancer risk. Evidence suggests that vitamin D deficiency may be responsible for poor muscle strength after bone fracture. The deficiency is associated with high blood pressure and diabetes, but it is unknown whether supplementation with vitamin D impacts these diseases.

Lower level of vitamin D have been associated with early age-related macular degeneration (AMD).

People at risk for deficiencies

Older people, particularly if they live in the North, who are underexposed to sunlight. Obesity may also increase risk. There is some concern, in fact, that vitamin D deficiency may be a growing problem in the US among younger adults as sunscreen use becomes widespread. Individuals at highest risk for vitamin D deficiency are those who assiduously avoid the midday sun, wear protective clothing, regularly use sunscreen, and have dark skin. Exposure to sunlight for about 15 - 20 minutes at mid-morning or mid-afternoon three times a week is recommended for most people who live in temperate climates.

Toxicities

Vitamin D is very toxic in high doses. In infants, daily amounts higher than 1,000 IU can cause mental and growth retardation, kidney failure, and death. In children and adults, daily amounts over 50,000 IU can cause weakness, anorexia, vomiting, diarrhea, and mental changes. Prolonged use of megadoses can cause calcification of soft tissue and life-threatening kidney failure. Low-calcium diets and withdrawal from the vitamin can usually reverse the side effects except for kidney failure.

Other Vitamins

Vitamin E (Tocopherol or Tocotrienol)

Vitamin K

Benefits

A fat-soluble antioxidant vitamin that helps prevent cell membrane damage and may inhibit oxidation of LDL cholesterol (a process that increases its harmful effects on arteries). Researchers once thought that vitamin E might protect against cardiovascular disease. This theory has been debunked. However, vitamin E supplementation may reduce the risk of deep vein thrombosis (DVT) in women at risk for, or with a history of, DVT.

The most important function of vitamin K is its role in blood clotting and prevention of bleeding. The vitamin also contributes to maintaining healthy bones and healing fractures. Vitamin K is widely used in Japan to treat osteoporosis, and studies suggest it may be effective in treating rheumatoid arthritis.

RDA is 15 mg (22 IU) for all adults, including pregnant women. Nursing mothers need 19 mg (28 IU). (Supplements should be taken along with some oil or fat to be absorbed.)

Vitamin E is composed of 8 compounds (four tocopherols and four tocotrienols). Vitamin E is most often available as supplements of dl alpha tocopherol (a synthetic form).

Other vitamin E compounds may prove to be more active than the standard synthetic supplement. They include natural vitamin E, called d-alpha- or RRR-alpha-tocopherol succinate (VES). Other vitamin E compounds of interest are tocotrienol and beta and gamma tocopherol. Supplements that contain a combination of some of these forms may be most beneficial.

AI is 120 mcg/day in men over age 19 and 90 mcg/day in women over 19, including pregnant and nursing women. The AI for pregnant and nursing girls 18 and younger is 75 mcg/day. The AI for children aged 1-3 years is 30 mcg/day, for children 4-8 55 mcg/day, for children 9-13 60 mcg/day, and for teens 14-18 75 mcg/day.

Tocotrienol (a possibly beneficial form) is found in natural tropical oils. Palm oil sold in the US is refined and does not contain tocotrienol.

Best dietary sources are canola oil, cruciferous vegetables, and soybean oil. Good sources are beef liver, bran, and olive oil.

Also produced by bacteria in the intestines.

Effects of deficiencies

Deficiencies have not been established.

Easy bruising, bleeding. May increase the risk of hip fractures in women.

People at risk for deficiencies

Low-birth weight infants.

People who eat a low-fat diet.

People with medical problems such as Crohn's disease, cystic fibrosis, steatorrhea, and liver diseases (such as cirrhosis), which impair fat absorption.

People with abetalipoproteinemia, a rare genetic disorder that impairs fat metabolism.

Deficiency may occur in patients who have problems absorbing fats, such as those with cirrhosis, people who are on long-term antibiotic therapy, or who are taking other medications, including cholestyramine, Dilantin, and phenobarbital. Some evidence suggests that more young people may be deficient than previously believed.

Toxicities

Upper level recommended is 1,000 IU of alpha tocopherol. Large doses may cause bleeding problems, particularly in people taking anti-clotting medications. Some research now indicates that vitamin E, like other antioxidants, may have pro-oxidant and damaging effects. Although vitamin E is one of the best studied vitamins, research has yielded conflicting results, and definitive conclusions about the benefits and toxicity of vitamin E have not yet been determined. In one major study, there was no significant difference in cancer rates between people who took 400 IU of vitamin E daily and those who did not, although those who took the supplement had a higher risk of heart failure. Additional studies also link high levels of vitamin E with a slightly increased risk of heart failure and death.

Allergic-type responses, including rash and itching, to high doses have been reported. Those who are taking Coumadin, an anticoagulant, should not take vitamin K without consulting a physician. Vitamin K deficiency can cause anorexia, lethargy, growth retardation, bone loss, soft tissue calcification, and death.

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